Self-levelling lamps

ABSTRACT

A headlamp self levelling system including front and rear body angle signals sent to a mixing unit for combination as a single lamp tilting signal which may be suitably damped. The mixing unit may comprise two springs working in opposition in a common housing. The lamp motion is damped by a force which may be greater when resisting lamp raising than when resisting dipping, or alternatively may be greater when resisting fast deflections than when resisting slow deflections. The lamps may be mounted on a two point support, one of which points is a ball and socket device and that or the other point will include a spring detent connection.

United States Patent 119 Martin 1 Feb. 25, 1 975 SELF-LEVELLING LAMPS [76] Inventor: Frederick Raymond Patrick Martin,

19 Hope Park, Bromley, Kent, England [22] Filed: Jan. 30, 1973 [21] Appl. No.: 328,057

Related U.S. Application Data [63] Continuation of Ser. No. 51,139, June 30, 1970,

abandoned.

[30] Foreign Application Priority Data July 1, 1969 Great Britain 33293/69 Apr. 22, 1970 Great Britain 19361/70 [52] U.S. Cl 240/7.1 LJ, 240/62 [51] Int. Cl. B60g 1/10 [58] Field of Search 240/7.1 L], 41.6, 52 R, 240/57, 62, 62.3, 62.6, 62.62; 248/291, 481, 483

[56] References Cited UNITED STATES PATENTS 1,382,728 6/1921 Holman et al. 240/4l.6 1,521,769 l/1925 Hillyer 240/41.6

2,105,866 1/1938 Sheaffer 240/62 R X 2,230,853 2/1941 Wells 240/41.6 X 2,984,737 5/1961 Marcellus 240/7.1 LJ 3,316,397 4/1967 Yssel 240/7.1 LJ 3,370,162 2/1968 Henry-Biabaud 240/62.62 X 3,453,424 7/1969 Cibie 240/7.1 LJ 3,504,171 3/1970 Martin 240/4l.6 X

Primary ExaminerFred L. Braun Attorney, Agent, or Firm-Fleit & Jacobson [57] ABSTRACT A headlamp self levelling system including front and rear body angle signals sent to a mixing unit for combination as a single lamp tilting signal which may be suitably damped. The mixing unit may comprise two springs working in opposition in a common housing.

The lamp motion is damped by a force which may be greater when resisting lamp raising than when resisting dipping, or alternatively may be greater when resisting fast deflections than when resisting slow deflections. The lamps may be mounted on a two point support, one of which points is a ball and socket device and that or the other point will include a spring detent connection.

7 Claims, 15 Drawing Figures PATENTEDFEBBS I975 SHEET 01 HF 10 Inventor FreJcw'ck RBR Ma l/,

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PATENTEUFEBPS ms 3,868,500

SHEET 0 2 [1F 10 PATENTEUFEBZSHTS I 3868500 SHEET D30F 10 PATENTEDFEBZS I975 SHEET OUUF 1O pm N 3 Ni PATENTFDFEBQS I975 SHEET OSUF 1O PATENTED FEB 2 5 I975 SHEET lUQF 10 SELF-LEVELLING LAMPS This is a continuation, of application Ser. No. 51,139, filed June 30, 1970, now abandoned.

The present invention relates to an improved form of self-levelling lamp system, and in particular to a selflevelling system in which the elevation of the lamp the springs having spaced points of connection to the rear body angle signal transmission member and the output signal transmission member, and the other spring having spaced points of connection to the front body angle signal transmission member and the output signal transmission member, the two springs being stressed in opposition to'each other in use of the device.

According to a second aspect of the invention there is provided a vehicle lamp self-levelling system comprising front and rear body angle signal generators and a mixer unit producing a single output signal for lamp angle controlling movement, and including at least one adjuster in the system between the mixer unit and the lamps for varying the gearing between the mixer unit output signal movement and the resulting lamp angle deflection, whereby the response rate of the lamps may be varied.

According to a third aspect of the invention there is provided a vehicle lamp self-levelling system comprising means for sensing the angle of the vehicle body relative to the plane of the ground wheels, means for effecting raising and lowering of the vehicle lamps in response to said angle to retain the lamp beams at the same angle relative to the plane of the ground wheels, and a damper for resisting lamp raising movement above a given deflection rate corresponding to passage of one or more wheels over a violent bump, but allowing lamp raising movement to correct for body angle changes of a lower deflection rate.

According to a fourth aspect of the present invention we provide a vehicle lamp self-levelling system comprising means for sensing the angle of the vehicle body relative to the plane of the ground wheels, means for raising and lowering the angle of vehicle lamp beams in response to variations in the angle sensed by said sensing means, and damping means comprising a pivotable lever forming part of the linkage between the sensing means and the lamps and a damper connected between a mounting fixed to the vehicle body and a point of connection on the lever, means being provided to move the said point of connection towards and away from the fulcrum of the lever for varying the damping effect.

According to a fifth aspect of the present invention there is provided a vehiclelamp self-levelling system comprising means for sensing the angle of the vehicle body relative to the plane of the ground wheels, means for raising and lowering the angle of the vehicle lamp beams in response to the sensing means, a linkage transmitting a lamp deflecting signal between said sensing means and said lamp raising and lowering means. and means operable by a vehicle occupant for varying the linkage independently of the signal transmitted from the sensing means whereby the vehicle occupant may adjust the angle at which the lamp beams are controlled in response to a predetermined angle sensed by the sensing means.

According to a sixth aspect of the invention we provide a vehicle lamp self-levelling system including at least one lamp support, a lamp unit adapted to be connected to said lamp support by means of two spaced pivotal connections at least one of which is a spring detent connection, and either the said at least oneor the other connection comprising a ball and socket connector, and a lamp control linkage for effecting pivoting of said lamp unit about a pivot axis passing through said two connections, means being provided for adjusting a selected one of said connections towards and away from said lamp support for deflecting the lamp unit beam 'axis about an axis perpendicular to said pivot ax1s.

According to a seventh aspect of the invention we provide a vehicle lamp self-levelling system which includes an elongate member extending between the vehicle rear axle and a signal mixer unit at the front of the vehicle for transmitting to the mixer unit a movement signal responsive to the height of the rear of the vehicle body above the rear axle, and a passage carried by a laterally deflectible steering component and through which passage said elongate member extends, said steering component being deflected whenever the steering is deflected from the straight-ahead position to cause said elongate member to transmit a lamp-dipping movement signal to said mixer unit.

According to a final aspect of the invention we provide a damper comprising a closed cylinder adapted to contain hydraulic fluid, a piston rod extending sealingly through one end of said cylinder, and a two part piston slidably connected to said piston rod between spaced lands thereof, means being provided for bearing the two parts of said piston axially outwardly against said lands, and said parts of the piston each including a disc portion having an outer periphery arranged to be closely adjacent the cylinder wall and provided with at I least one passage disposed radially inwardly of said perimeter portion but arranged so as to be non-alignable with the corresponding passage or passages of the other piston part.

In order that the present invention may more readily be understood, the following description is given, merely by way of example, reference being made to the accompanying drawings in which:

FIG. 1 is a side elevational view of a self-levellin headlamp system in accordance with the present invention;

FIG. 2 is a detailed, partly sectional view showing the add and subtract box of FIG. 1;

FIG. 3 is a view, similar to FIG. 1, but on a reduced scale and showing an alternative embodiment of transmission linkage;

FIG. 4 is a plan view showing the lamp of FIGS. 1 t 3 and illustrating clearly the quick release lamp mounting system;

FIG. 5 is a front elevational view of the lamp of FlG.

FIG. 6 is a detailed view of the horizontal direction adjustment unit shown in FIGS. 4 and 5;

FIG. 7 is an underneath plan view showing an alternative embodiment of elevation and response ratio adjustment unit;

FIG. 8 is a side sectional view showing a modified form of signal mixer unit;

FIG. 9 is a side elevational view showing the mixer unit of FIG. 8 incorporated in a self-levelling system similar to that of FIG. 3;

FIGS. 10a and 10b illustrate a modified form of quick release lamp fitting and represent schematic front elevational and side sectional views, respectively;

FIG. 11 is a side view, mainly sectional, and showing a manual lamp beam elevating mechanism for cooperation with the self-levelling system of either FIGS. 1 to 3 or FIGS. 8 and 9;

FIG. 12 is a side elevational view illustrating the derivation of a rear body angle signal on a vehicle implying a DeDion type of-rear axle and showing a much simplified front linkage between the signal mixer unit and the lamp cross tube;

FIG. 13 shows a side sectional view of a modified form of shock-absorber suitable for use in the selflevelling system of either FIGS. 1 to 3 or FIGS. 7 and 8; and

FIG. 14 shows a section through the cross member of a preferred form of linkage similar to that of FIG. 12.

Referring now to the drawings, and in particular to FIGS. 1 to 3 which show a first embodiment of selflevelling headlamp system comprising a headlamp l pivotally mounted at 2 for tilting about a horizontal diametral axis, and mounted within a surrounding body structure 3 of a vehicle such as an automobile within which the self-levelling headlamp system is installed. In the specific embodiment illustrated in FIGS. 1 to 3 the vehicle is a motor car and has a radiator 4 in front of which an array of lamps, including the lamp 1, is positioned. The upper part of the lamp periphery abuts against a spring biased damper unit 5 secured to the vehicle body structure 3, and the lower part of the lamp includes a bracket 6 which is pivoted by way of a mechanical contact stud comprising a screw 7 and nuts 8 and 9, by pivoting movement of an associated tongue 10 projecting radially outwardly of a linking cross member I] in the form of a rod or tube extending transversely across the front of the vehicle mounted in suitable bearings (not shown). It will be apparent from FIG. 1 that rotation of the cross member or tube I1 in a clockwise sense will result in increase in elevation of the lamps 1, whereas anti-clockwise rotation of the cross member 11 will permit the spring-biased damper unit 5 to effect dipping or decrease in elevation of the lamps.

Rotation of the cross member 11 is effected by way of a linkage comprising a signal mixer unit 12 which combines mechanical signals corresponding to rise and fall of the front and rear of the vehicle, to create a single output signal at a thrust pin 13 riding in a clevis 14 at the end ofa rocking arm 15 pivoted to a bracket 16 riveted to a bulkhead 17 of the vehicle.

The signal of rear body raising and lowering movement is derived by way ofa cable 18 extending from the signal mixer unit rearwardly substantially parallel to the vehicle axis, over a rotatable pulley and secured to a point near the top of the casing of the rear axle differential unit, the pulley and differential casing attachment point thus serving as a rear body movement signal generator. Any tail-down movement at the rear of the vehicle will result in the body mounted pulley descending while the axle mounted cable end retains its position and the length of the cable run between the pulley and the point of securing to the differential casing will increase to effect rearward movement of the cable 18.

The signal corresponding to rise and fall of the front ofthe vehicle is derived from a lever 19 secured to the anti-roll bar 20 of the vehicle so that a nose-down movement of the front of the body will result in clockwise rotation of the anti-roll bar and corresponding clockwise pivoting of the lever 19.

For example, if both the front and rear of the vehicle descend together the headlamp beam elevation will be required to remain substantially constant since the angle of the vehicle body with respect to the mean plane of the road surface will remain constant and there will therefore merely be a slight tendency for the headlamp beam to shorten since the headlamp units 1 are now closer to the road surface. In such a situation the lever 19 will pivot clockwise and the cable 18 will move rearwardly and the net result at the output end of the signal mixer unit will be a substantially unchanged signal which will retain the headlamp elevation at the desired value. The precise operation of the mixer unit will be described more fully below with reference to FIG. 2, but it will appreciated from the foregoing that the fore and aft movement of the thrust pin 13 will, due to the functioning of the mixer unit, provide a rectilinear displacement signal the direction and extent of which will represent the sense and angular displacement of the body in the nose upward and nose downward directions. Nose-upbody tilt will result in rearward movement of the thrust pin 13 and vice versa. The upper end of the rocking arm 15 is linked to a further tongue 21 of the cross member 11 by means of a helical tension spring 22 connecting appropriately placed locations 21a on the tongue and 15 a on the rocking arm.

The spring-biased damper unit of FIG. 1 comprises a closed ended tube 23 secured to the vehicle frame and enclosing a compressing spring 24 and a loose fitting plunger 25 urged rightwardly by the spring 24. The space within the tube 23 is filled with hydraulic fluid and the outer end of the tube is sealed by means of a bellows 26 so that, upon rightward movement of the piston 25, hydraulic fluid will move Ieftwardly along the clearance between the plunger 25 and the tube 23. Clearly the motion of the plunger will be biased rightwardly and will be damped by the flow of the hydraulic fluid. It will be appreciated that each of the headlamps 1 of an array driven from the torque rod or tube 11 will be provided with its own damper unit 5.

However, it is equally possible for the self-levelling system to be constructed so that a single damper unit serves to control the entire system as shown in FIG. 3 where the spring-biased damper unit 44 mounted on the bulkhead l7 acts upon an arm 47 to damp rotation of the cross member 11. The positioning of the spring 69 again ensures that the spring-biasing effect is tending to assist lamp dipping movement. The arrangement of FIG. 3 has a further advantage that the fulcrum point 46 of the shock absorber strut 45 on the arm 47 can be moved towards and away from the axis of the cross member 11, thereby varying the extent of the damping moment exerted by the single shock absorber. An alternative form of shock absorber which exhibits the same effect of providing a higher resistance in one direction than in the other would be one in which the spring 69 were omitted but the piston were provided with a throughbore and non-return valve so that piston movement in a first direction would open the non-return valve and cause hydraulic fluid to flow along the piston throughbore with low flow resistance, whereas piston movement in the opposite direction would close the non-return valve and effectively increase the flow resis tance. Yet a further form of shock absorber suitable for the present system is illustrated in FIG. 13 and will be described in greater detail hereafter.

Turning now to FIG. 2, there is shown a detailed view of the mixer unit 12 which consists of an outer tube 27 having slidable inner tubular pistons 28 and 29 at the rear and front ends thereof. The rear piston 28 is provided with a pair of diametrically opposed outwardly extending pegs 30 which engage in diametrically opposed longitudinal slots 31 of the outer tube 27. Driving movement of the rear piston 28 is effected by way of engagement between a bifurcated upper end 19a of the anti-roll bar lever 19 engaging against the pegs 30 to urge them in a rightward direction.

Rightward movement of the rear piston 28 is transmitted to the front piston 29 by way of an outer helical compression spring 32 disposed within the tube 27 between the pistons.

The signal from the rear of the vehicle via the cable 18 is introduced to the front piston 29 direct by way of a helical tension spring 33 the rear of which is secured to the front end of the cable by means of a clevis assembly 34. The hollow front piston 29 carries an integrally formed outwardly extending lug 35 supporting the thrust pin 13 for engagement with the clevis 14, and

also an inwardly extending tab 36'provided with an ap erture 37 within which the front end of the tension spring 33 may be received. The outer tube 27 is provided with an integrally formed L-shaped bracket 38 which serves as a mounting for the fulcrum of rocking arm 15.

The spring rates and geometry of the mechanism are so chosen that both front and rear of the vehicle may descend by the same distance and the ensuing modified compression of spring 32 and the modified tension in spring 33 will provide equal and opposite forces acting on the front piston 29 in a direction axially of the tube or cylinder 27. However a nose-up pitching tendency will result in an increase in tension of spring 33 and a reduction in compression of spring 32 causing a simultaneous leftward movement of the front piston 29, and likewise a nose-down pitching tendency will cause rightward movement of the front piston 29. It will be appreciated that the springs 32 and 33 are prestressed upon assembly of the mixer unit 12, to ensure that spring 32 is always under compressive strain and spring 33 under tensile strain for all possible values of front and rear body angle signals.

The screw 7 in the lock nuts 8 and 9, as illustrated in FIG. 1, provides a dual adjustment facility in that adjusting the screw by rotation within the lock nuts while maintaining the same position radially of the lamp unit will alter the neutral setting of the lamp, i.e. screwing in will raise the lamp beam for a given position of the vehicle body and screwing out will result in lamp dipping. However, additionally the screw 7 extends through a slot in the bracket 6 permitting adjustment of the position of the screw radially of the lamp unit,

thus varying the relative effective lever arms of the engaging bracket 6 and tongue 10 and enabling a variation in the gearing ratio between the output signal from the mixer unit and the lamp angle change resultant therefrom. For example raising of the screw 6 will increase the lamp angle change for a given output signal from the mixer unit, and loweringof the screw will decrease the lamp angle change.

By providing the ratio adjustment mechanism 7, 8,9 at the individual lamp rather than on the cross member 1 1, it has been ensured that, if desired, individual lamps driven from the same torque tube may have deliberately differing response ratios, if desired.

FIG. 1 shows the existence ofa shroud 38 which conceals the ratio adjustment and mechanical contact stop screw 7 and thereby eliminates the possibility of inadvertent damage to, or unauthorised tampering with, the screw 7. Clearly such a shroud 38 will be made readily removable in order to provide easy access to the screw 7. The shroud 38 will also serve as a rotation limiting stop to limit the extent of increase in elevation of the lamp 1, apart from exhibiting certain decorative advantages. A similar purely decorative shroud is provided at 39 adjacent the topv of the headlamp unit.

Clearly, some form of adjustment mechanism, for example a screw adjuster in the cable 18, may be provided in order to ensure that the two springs 32 and 33 of the mixer unit are comfortably balanced when the remainder of the linkage is conveniently adjusted.

The tension spring 22 may be replaced by a transversely extending limb adjustably mounted on the arm 21 by means of a slidable collar surrounding the arm 21 and lockable by means of a grub screw. The free end of the limb would be of bifurcated construction and provided with a roller which engages against the rear of the rocking arm 15 received within the bifurcated end. Thus, upon movement of the collar and limb axially of arm 21, the roller will ensure a self adjusting engagement with the rocking lever.

Turning now to FIG. 3, it would be appreciated that the mechanism is substantially identical with that of FIGS. 1 and 2, except that the tongue 21 and tension spring 22 have been replaced by a single leaf spring 41 secured to the cross member. In this instance adjustment of the-imbalance from the mixer unit springs may be effected by raising and lowering the contact stud 42 on the rocking arm 15.

Moreover, in the embodiment of FIG. 3 the individual spring-biased damper units 5 have been replaced by straightforward spring-loaded anti-flutter assemblies 43 to maintain contact between the tongue 10 and screw 7, a single damper or shock absorber 44 being provided as described above.

In FIG. 1 and 3, the headlamp unit 1, when in position, is acted upon from the rear at two points by on the one hand the spring damper unit 5 and on the other hand the tonuge 10. This arrangement, together with the simple quick release attachment on the control horizontal pivot axis of the lamp enables a very rapid and convenient installation procedure to be devised for the lamp unit 1.

The quick release installation system of the headlamp unit 1 is shown in FIGS. 4, 5 and 6. The plan view of FIG. 4 shows the lamp unit 1 provided on a horizontal diameter with, at one end a ball 48 mounted on a peg 49 and engageable with a suitably disposed cup 50 on a similar peg 51 secured to the vehicle body, and at the other end with a spring-loaded tube arrangement 52 which can engage over an adjustable peg 53 to provide for horizontal directional adjustment of the headlamp. The peg 53 and associated adjustment device are shown more clearly in FIG. 6, but the front elevational view of FIG. illustrates an adjustment screw 54, rotation of which effects fore and aft movement of a suitable trunnion including the peg 53, and thus, due to cooperation with the fixed cup 50, results in adjustment of the horizontal adjustment of the beam from the headlamp unit 1.

FIG. 6 shows, in greater detail, the adjustment trunnion 55 in the form of a solid cylinder having two diametrically opposed outwardly extending pegs 53 and 56, the peg 53 being longer and being positioned for engagement with the spring-loaded tube 52 on the lamp unit. The shorter peg 56 serves merely to restrain the trunnion against rotation within an outer cylinder or chamber 57, and this restraint is assisted by the action of the longer peg 53 in that both of the pegs cooperate with longitudinally extending slots 58 and 59 formed in the cylinder body. A helical compression spring 60 bears against an end wall of the chamber 57 and urges the trunnion 55 outwardly against the shank of the ad justment screw 54, and clearly the axial positioning of the trunnion 55 within the cylinder or chamber 57 is thus achieved by rotation of the screw 54. The chamber 57 is provided with a suitable mounting bracket 61 which can be fastened to the vehcicle body by riveting, screwing or any other suitable means. Thus, by adjustment of the screw 54 the peg 53 may be moved in the fore and aft direction so that the central horizontal axis of the lamp is rotated about a substantially vertical axis to effect adjustment of the direction of projection of the headlamp beam.

FIGS. a and 10b show an alternative form of lamp mounting system employing two similar connectors 190 in the from of cups 191 engaging balls 192 and thus the lamp unit 185 is mounted with relation to the cell 189 for pivotal movement about its horizontal axis. One or both of the connectors 190 may be adjustable, for example by means of the nut 194 and the screw shank 193 of the bore so that the angle of the beam about a vertical axis may be adjusted.

In an alternative form of quick release lamp mounting which is particularly suitable with the linkage of FIG. 12, one of the ball and socket connections 190 may be replaced by a sideways facing connector which can engage with the control linkage cross member extending between the lamps to provide a driving engagement whereby the lamp beams may be raised and lowered upon rotation of the horizontal cross member. Such a driving engagement may be provided by using a ball joint connection between the cross member and lamp but with a pin extending through the ball and engaging with a pair of diametrically opposed tapered grooves extending longitudinally of a tubular cross member.

FIG. 7 shows a view, corresponding to an underneath plan view of the response ratio and lamp elevation adjustment mechanism of FIG. 1, but illustrates instead an alternative construction of adjustment mechanism which provides quite separate adjustment facilities for the lamp elevation and mechanism response ratio. The adjustment'mechanism 62 is secured to the bracket 6 extending radially outwardly from the head lamp, as in the FIG. 1 embodiment, and comprises a lamp elevation adjustment screw 63 which may be rotated by means of the hexagonal head 64 and locked by a hexagonal lock nut 65 engaging against one end of an internally and externally threaded tube 66. The tube 66 engages slightly within the narrower of a pair of longitudinally extending slots on the bracket 6 and may be locked at any particular location along the bracket to provide a locked response ratio setting. The elevational adjustment of the headlamps is then effected by loosening the lock nut 65, rotating the head 64 of screw 63 by means of a suitable spanner device, and then once the appropriate headlamp elevation setting has been obtained, the lock nut 65 is retightened to clamp the screw 63.

The tube 66 is locked at any particular response ratio setting by means of a hexagonal nut 67 engaging against one side of the bracket 6 and a square headed nut seated within the wider of the two slots disposed on the opposite side of the bracket 6. Adjustment of the response ratio setting is effected by slackening the hexagonal lock nut 67, movement of the tube 66 longitudinally of the double slotted bracket 6 to the desired response ratio positioning, and then retightening of the lock nut 67 to clamp the tube into position. Once the response ratio setting has been adjusted it may be necessary to readjust the elevational setting by means of lock nut 65 and screw head 64.

The above described self-levelling headlamp system may be further modified in order to provide an automatic dipping facility upon deflection of the steering. Such a modification may include some form of deflection of the rear body movement signal cable 18 upon movement of the steering, and a particularly suitable means of effecting this deflection would be the provision of a bell crank one arm of which has a clevis end for engagement with a suitable pin on the vehicle steering linkage, the other arm of which is provided with a grommet or nylon bush through which the rear body movement signal cable 18 passes. The bell crank is best orientated so that, when the steering is in the dead ahead position the nylon bush or grommet is disposed so that the rear body movement signal cable is taut and undeflected. Thus, upon deflection of the steering to one side of the dead ahead position the nylon bush will deflect the cable 18 away from its straight line condition and upon reverse steering deflection the bush will be displaced in the opposite direction by an equal distance, thereby simulating a rear body lowering signal and effecting dipping of the headlamp units 1 of the ve hicle.

FIGS. 8 and 9 show an alternative form of mixer unit and from these Figures it may be seen that the rear vehicle body signal transmitted from the rear axle via a cable or flexible rod 118 is transmitted to a tube 171 by way of threaded engagement with a threaded end 170 of the cable or rod 118. The front vehicle body signal is transmitted by way of a lever 119 secured to the vehicle anti-roll bar having a bifurcated end 119a engaging a pair of stub pins for urging the tubular housing 127 of the mixer unit in a rightward direction. It can be seen that one essential difference between the device illustrated in FIG. 8 and that of FIGS. 1 to 3 is that the tubular housing 127 in this embodiment is freely suspended between the cable 118 and the antiroll bar lever 119, whereas in the earlier embodiment the housing is bolted to a convenient part of the vehicle body.

The two springs of the mixer unit are arranged end to end such that the front body signal spring 132 is arranged rearwardly of the rear body signal spring 133. The front body signal spring 132 is compressed between, at the one end a slide disc 129 which is disposed between the adjacent ends of the two springs 132 and 133, and at the other end an inwardly extending flange 172 secured to the tubular housing 127 to define an abutment surface. Likewise, the rear vehicle body signal spring is compressed between the slide disc 129 and a radially outwardly extending flange 173 formed at the front end of the tube 171. Thus the arrangement is such that tightening of the rear vehicle body signal cable 118 will compress the spring 133 and urge the slide disc 129 leftwardly while clockwise movement of the anti-roll bar lever 119 will move the tubular housing 127 rightwardly and thereby compress the spring 132 moving the slide disc 129 rightwardly. Since tightening of the cable 118 corresponds to downward movement of the rear of the vehicle, and clockwise movement of the antiroll bar arm 119 corresponds to downward movement of the front of the vehicle, the geometry of the various components will be arranged such thattequal downward movement of front and rear of the vehicle will leave the slide disc 129 static in relation to the vehicle body.

Although the drawings illustrate two separate compression springs 132 and 133, it will be appreciated that the mixer unit may equally comprise one long spring with an output signal connection at a point intermediate its ends dividing the spring into two separately acting spring portions.

Movement of the slide disc 129 will be transmitted to the lamp angle signal output rod 135 by way of a pin 174 which extends snugly through the disc 129 and the rod 135 and slidably through diametrically opposed slots 175 of the tube 171. The front of the lamp angle signal output rod 135 is connected to the lamp control linkage by way of an articulation connection which is shown more clearly in FIG. 2.

In FIG. 9 the articulation connection just referred to is referenced 176 and connects the rod 135 with one limb 177 of a bell crank, the other limb 178 of which is articulated to a vertically movable strut 179 articulated at 180 to a lever 181 between its fulcrum point 182 and its free end which is articulated at 183 to a telescopic fluid-filled damper unit 184.

The lamp unit 185 is mounted for pivotal movement about a horizontal axis and is provided with a tab 186 which engages with a further lever 187 having a common fulcrum with the lever 181.

In practice the fulcrum 182 consists of a cross member extending transversely across the vehicle and linking the various headlamps and/or spot lights at the front of the vehicle so that they may all be levelled by the single linkage comprising components 176 to 184.

The cross member 182 may either be connected across the vehicle beneath the vehicle radiator in such a way the cross member is carried by bearings secured to the vehicle front sill, or alternatively the cross member 182 may be carried by bearings mounted in the two headlamp nacelles of the vehicle in which case the member 182 is disposed at a much higher location in the vehicle. Such an arrangement is shown in FIG. 12.

As in the embodiment of FIGS. 1 to 3, the shock absorber or damper unit 184 is arranged to exert a much higher viscous drag in one direction than the other, in

this case the higher drag is exerted during compression of the shock absorber. This may be achieved by providing a one-way flow permitting valve in the piston of the shock absorber so that during compression of the shock absorber the flow of damper fluid will close the oneway valve and thus damper fluid will have to be transferred around the edges of the piston, whereas during extension of the shock absorber the flow of damper fluid will open the one-way valve and thus a much lower viscous drag will be exerted on the fluid.

It will be appreciated that, by virtue of the slow compression but rapid extension of the shock absorber 184, the lamp unit can be dipped rapidly but will be much slower in rising. Thus, in the event of the vehicle striking a rough road surface the lamp will tend to overdip and will thus not be subjected to violent lamp flutter which might otherwise be the case if the vehicle vibration were of sufficiently high frequency to defeat the lamp levelling system.

Since it is a common characteristic of automobile shock absorbers that they offer a higher resistance force to movement of the body towards the wheels than to movement of the body away'from the wheels, it is usual for the beams of conventional fixed headlamps to rise very rapidly but to descend more gradually and thus there is a strong likelihood of dazzling oncoming or preceding traffic. For this reason the doubleresistance shock absorber is considered a particularly desirable feature of the present invention.

A further advantageous feature of the doubleresistance shock absorber is the face that its point of articulation 183 with the lever 181 can be varied in order to alter the damping moment exerted on the lever 181. Although, once the characteristics of the system have been evaluated, it will be possible to determine the correct positioning for the shock absorber articulation point 183 it is desirable for some adjustment to be possible to compensate for varying damper fluid viscosities in response to varying ambient temperatures. Thus the lever 181 may bear calibrated graduations corresponding to different mean ambient temperatures and the position point of articulating 183 can then be varied, for example by articulation the shock absorber to a sliding collar on the lever 181 so that sliding of the collar along the lever will vary the moment arm of the shock absorber on the lever 181. Additionally, more than one possible location for the upper articulation point 188 may enable the shock absorber to be positioned such that its line of action is always perpendicular to the neutral position of the lever 181.

A further embodiment of shock absorber is illustrated at 205 in FIG. 13, and in this instance comprises an oil filled cylinder 206 having an end cap 207 through which a piston rod 208 sealingly extends. The piston 209 is of bipartite construction comprising a cup member 210 and a plate 211 which are slidably urged apart between upper and lower lands 212 and 213, respectively, by means of a compression spring 214. The disc member 211 includes four equiangularly spaced passages 215 and the cup member 210 has a radial outwardly extending flange or disc portion including four further equiangularly spaced passes 216 which are at a different radius from the passages 215 so that hydraulic fluid passing between the regions above and below the bipartite piston 209 follow a tortuous path through the respective passages 215 and 216. Clearly, the closer the disc member 211 comes to the flange of the cup memher 210, the more tortuous will the flow path become.

Slow upward and downward movement of the piston rod 208 will cause oil to bear against the respective one of either the upper face of the disc member 211 or the lower face of the flange of the cup member 210, tending to urge the disc and the cup together against the action of the spring 214. However, the spring rate of the spring 214 is of such a value that slow piston movements up to a predetermined rate of movement will be unable to overcome the compression spring 214 and will therefore be resisted by the lighter resistance force experienced when the hydraulic oil follows the less tortuous flow path shown in FIG. 13. Once that predetermined rate of movement is exceeded the dynamic pressure forces of the fluid against the disc or the cup will urge the disc or the cup towards and substantially into contact with the other of the two members causing the flow path to become more tortuous and providing a much higher resistance to piston movement. Thus, the shock absorber of FIG. 13 is one which will permit slow lamp deflecting movements to be conveyed through the linkage but will resist movements of higher rates, for example those resulting from vehicle wheel flutter as the vehicle runs over a rough surface. Thus the lower frequency movements needed to correctbody movement of the vehicle will be passed to the lamps whereas the higher frequency movements correcting for wheel flutter will be damped. In this way the damper or shock absorber achieves the same result as that required in the earlier embodiments employing one-way shock absorbing action except that in this instance there will be no need for the overdipping of the lamps on a rough surface since the system will never be defeated and the lamps will always be correctly controlled.

The shock absorber of FIG; 13 may be positioned at any conventional part of the linkage and in the preferred linkage of FIG. 12 the shock absorber will be arranged to bear against an arm extending radially outwardly of the cross member 220 extending between the lamps. However, for reasons of simplicity of the drawing the shock absorber has been omitted from FIG. 12.

Where the vehicle rear axle is of the semiDeDion type, there will be no need for the cable to pass over a pulley wheel secured to the underside of the vehicle body since the semi-DeDion of axle executes a movement which is a combination of vertical and horizontal components. Thus upward and downward movement of the vehicle body with relation to the ground will result in a simultaneous fore and aft component of movement of the axle and this may be sufficient to provide the necessary movement of the rear vehicle body signal cable 118.

An alternative way of deriving the rear body angle signal from a semi-DeDion type of axle is illustrated in FIG. 12 where one wheel 240 of the vehicle is mounted on an arm 241 which is itself pivoted to the vehicle body at 242. The rear body angle signal linkage comprises a sensing arm 243 pivotally mounted to a bracket 244 on the underside of the vehicle body and resting on the arm 241 of the axle mechanism. A downwardly extending portion 255 of the sensing arm is provided at its lower end with a ball and socket connector 246 to transmit to a strut 247 the fore and aft movement of the sensing arm extension 245 resulting from upward and downward movement of the wheel and hence of the sensing arm itself. The front end of the strut 247 passes slidably through a bracket 248 and is connected to the front end of a Bowden cable assembly 249 which transmits the signal to the floating type of mixer unit similar to that described in detail in FIGS. 8 and 9.

FIG. 11 shows a driver operated beam angle adjuster unit comprising a Bowden cable extending between a push-pull control unit on the vehicle dashboard and the headlamp self-levelling linkage, in particular to a lever 181 driven by the output signal from the mixer unit and the lamp driving crank 187.

The Bowden cable outer casing 196 is secured to a housing 196a attached to the vehicle dashboard 197 at one end and to one of the lever 181 at the other end, and the cable inner is secured to a push-pull button 198 at the dashboard end and to a stub lever 187a formed integrally with the main lamp tilting crank 187 of FIG. 9

Clearly, as the push pull control 198 is pulled away from the dashboard, i.e. leftwardly as viewed in FIG. 11, the stub lever 187a will move towards the lever 18] and will thus urge the lamp tilting crank 187 in the anticlockwise direction to a new position which will correspond to a lower beam angle for a given output signal from the mixer unit output rod 135.

The dotted lines referenced A, B and C at the pushpull control 195 represent alternative positions of the push-pull control button 198 and a suitable mechanism device will be provided for ensuring that the positions A, B and C, and the solid line position 198 illustrated in FIG. 11 are distinct settings to which the push-pull control button 198 can always be returned. For example, the housing 196a to which the end of the Bowden cable outer'casing 196 is connected may have four recesses formed in its inner wall for engagement with a suitable spring-loaded ball in the shank of the push-pull button 198, so that fixed positions are defined by engagement of the spring-loaded ball with the respective recesses. The solid line position illustrated corresponds to a fog position, position A corresponds to the conventional dipped beam" position, position B corresponds to the conventional main beam position, and position C corresponds to a long beam position in which the beam may be set to a substantially horizontal setting for extremely long range vision ahead of the vehicle. Naturally, the use of such a long range setting will depend upon local traffic regulations, but it is envisaged that the extremely accurate self-levelling control of the lamps will enable a beam to be set to a substantially horizontal position without any danger of dazzle to oncoming or preceding traffic.

Since the Bowden cable executes a free loop between the point of attachment of the lever 181 and a grommet 199 in a suitable bulk head 200, the Bowden cable will not impede the normal operation of the self-levelling linkage. Thus the mechanism provides simple means of adjusting the head lamp settings from within the vehicle without any deleterious effect on the normal operation of the self-levelling lamps.

The driver-operated beam angle adjuster of FIG. 11 may equally well be included with any of the embodiments of FIGS, 1 to 3 or FIG. 12 and it may be connected at any convenient point in the linkage. The precise manner of incorporation of the manual adjuster within any particular vehicle self-levelling system can readily be determined by any expert in this art.

The simplified mechanism of FIG. 12 is one in which the output signal from the mixer unit 221 is transmitted by way of a strut 222 which is connected to a further strut portion 223 by way of a ball joint 224. The further strut 223 has at its other end a ball joint 225 engaging with the lower end of a downwardly extending arm 226 carried by the cross member 220. A screw 227 enables adjustment of the precise positioning of'the arm 226 on the cross member 220 to adjust the vertical positioning of the lamps and, additionally, the arm 226 is of telescopic construction and has a lock nut-.228'=-by means of-which the selective length of the arm 226 can be held. Clearly, adjustment of the length of the arm 226 will provide the facility for adjusting the response ratio I of the lamp.

FIG. 14 shows a particularly suitable type of connection between the arm 226' and the cross member 220'. In this instance the arm 226' is carried by a sleeve 229 rotatably mounted on the vehicle body. The sleeve carries an internally threaded tangentially extending portion 230 within which the upper threaded end 231 of the arm 226 can engage. The cross member 220' extends coaxially through the sleeve 229 and is provided with an upwardly extending tab 232 which, together with a similar tab 233 secured to the sleeve 229 supports a screw 234 having a knurled head 235. The two tabs 232 and 233 are urged apart by a compression spring 236 which is sufficiently strong to provide an effective rigid link between the two tabs 232 and 233. This part of the adjustment mechanism will be situated adjacent the cross member 220 just behind the front grille of the vehicle so that adjustment of the screw 234 may be effected either by placing the screwdriver through the grille and engaging a suitable slot in the head 235 of the screw, or by inserting the fingers through the grille to rotate the knurled head 235, thereby effecting vertical adjustment of the assembly of two or more lamps controlled from the single cross member. The ratio adjustment is effected by placing a screwdriver in the top of the end 231 of the arm 226' to rotate the arm and cause effective raising or lowering of the arm within the bracket portion 230. Further adjustment of the lamps will be needed in that it will be possible to adjust the elevation of one lamp with respect to the other and this maybe achieved by providing the cross member in two parts, one of which plugs into the other in freely rotatable manner, the plug and socket portions being provided with respective radially outwardly extending tabs which are engaged by a common screw and are urged apart by a suitable compression spring. Thus adjustment of the screw through the tabs moving the tabs towards or away from one another will result in relative angular rotation of two parts of the cross member thereby enabling the two lamps of a set to be adjusted with respect to one another, for example, to provide a pair of level beams. Naturally, when adjusting such a system in practice, it will be necessary first to synchronise the lamps and then to adjust the vertical setting of the synchronised pair of lamps.

Any of the above described systems may be provided with ratio adjusters, and equally the ratio adjusters may be omitted in production systems where the precise geometrical characteristics required of the selflevelling system are known in advance. The system may therefore be constructed to operate in the desired manner upon installation in a particular known vehicle without the need for response ratio adjustment.

In some vehicle installations the anti-roll bar may be positioned very close to and vertically below the vehicle radiator. This would reduce the amount of space available for the anti-roll bar lever required by the front vehicle body angle sensing system in each of the above described embodiments. In such a case it is possible to employ the longest arm commensurate with the space available and to affect the balance of the signals by employing mixer unit front and rear body signal springs which have different spring rates. This may conveniently be achieved by employing springs of identical construction but of different lengths. In this way the effect of the front body angle signal may be magnified within the mixer unit so that a sufficiently large output signal may be derived to drive the lamps for levelling movement. Likewise, if required, the rear body angle signal may be amplified, for example by means of a suitable lever arrangement positioned under the vehicle body. One suitable such lever system can comprise a lever oriented substantially vertically and positioned under the vehicle rear seat but mounted on a bracket for rotation about a horizontal axis extending transversely of the vehicle. The rear body angle signal may then be derived by way of a cable from the rear axle to the upper end of the lever, and the signal is thus transmitted to the mixer unit by means of a further cable connected between the bottom lever and the mixer unit itself, if necessary, through the agency of a strut as shown at 247 in FIG. 12. By varying the distances between the lever fulcrum and the point of connection to the cables connecting it to on the one hand the rear axle and on the other hand the mixer unit, the rear signal may be amplified or attenuated at will.

FIG. 8 shows, in chain dotted lines, a pin 171a which engages with diametrically opposed holes in the tube 171 to act as a keeper, retaining the springs 132 and 133 appropriately stressed when the mixer unit is removed from the vehicle. Thus installation or reinstallation of the mixer unit will merely require hooking of the front end of the housing 127 over lever 119, connecting up to cable 118 and lever 177 (FIG. 9) and tensioning the cable 118 until the keeper pin 171a falls out, indicating that the system is connected and correctly tensioned.

I claim:

1. In a lamp self-levelling system comprising front and rear vehicle body angle signal generating means, and a lamp tilting linkage connected to at least one lamp to be levelled; signal mixing means operably connected to said vehicle body angle signal generating means and said lamp tilting linkage; a pair of springs in said mixing means operably connecting the lamp tilting linkage with respective ones of the front and rear body angle signal generating means; adjuster means in at least one of said front and rear body angle signal generating means for initially prestressing said springs; and indicator means responsive to the strain of said springs for indicating when the prestressing of said springs by said adjustor means has attained a strain value equivalent to a predetermined operating stress value.

2. A system as set forth in claim 1, wherein said signal mixing means includes a housing and an elongate member extending into said housing for connection to one of said springs, the other spring being connected to said housing, wherein said adjuster means is effective to modify the rear body angle signal to stress said springs and wherein said indicating means comprises a pin loosely extending transversely through said elongate member and frictionally held in position by the strain in said springs at a position such that adjustment of the rear body angle signal generating means to said predetermined strain will expand the springs and allow the pin to fall from the elongate member. I

3. A vehicle including a lamp self-levelling system, and comprising ground wheels and a body, at least one lamp to be levelled, means for sensing the angle of the vehicle body relative to the ground wheels, means for effecting pivoting of said at least one vehicle lamp about a horizontal axis in response to said angle to retain the lamp beam at a constant inclination relative to the ground wheels, and means for damping movement of said lamp, said damper comprising a cylinder having a longitudinal axis, a loose fitting two-part piston slidably mounted within said cylinder and a liquid damping medium within said cylinder damping movement of said piston along said cylinder, said piston comprising first and second parts, means biasing said first and second parts apart, respective through passage means in said first and second parts defining together tortuous fluid flow passage means, said piston parts being constructed with said respective through passage means arranged at different radial distances relative to the longitudinal axis of said cylinder.

4. A vehicle having a front suspension anti-roll bar extending transversely of the vehicle, a rear axle and a lamp self-levelling system comprising:

. a. at least one lamp to be levelled;

b. an arm extending vertically from the front anti-roll bar;

c. a cylindrical housing;

d. pivot means for hooking said housing to said arm at a location remote from the front anti-roll bar;

e. an output signal piston slidably carrie'd within said housing;

f. a lamp tilting linkage connected to said output signal piston and to said at least one lamp;

g. a first coil spring in said housing and having a first end connected to said output signal piston and a 7 second end connected to said housing;

h. a second coil spring in said housing and having first and secondends, said first end being operably connected to said output signal piston;

i. a cable having a first end operably connected to the second end of said second spring and having a second end disposed at a location on the vehicle remote from said housing; and

j. means operably connecting said second end of the cable with said rear axle for pulling said second end of the cable away from said housing in response to a vertical movement of the rear of the vehicle body.

5. A vehicle as set forth in claim 4 wherein said means operably connecting the second end of said cable with the rear axle comprises an L-shaped arm having a first limb resting on the rear axle and a second limb operably connected to said second end of the cable, and a bracket secured to the vehicle body supporting said arm for pivoting movement whereby raising of the vehicle rear ground wheels relative to the vehicle body effects rearward movement of said second limb relative to the vehicle body.

16 6. A vehicle as set forth in claim 4 and including a rear body angle signal transmission piston slidable within said housing, said second spring being compressed between said output signal transmission piston and said rear body angle signal transmission piston; and

a front body angle signal transmission abutment member secured within said housing, the said first spring being compressed between said output signal transmission piston and said front body angle signal transmission abutment member.

7. A vehicle having a lamp self-levelling system comprising:

a. at least one lamp to be levelled;

b. a cylindrical housing; I

c. first and second springs in said cylindrical housing and each having first and second ends;

(1. an output signal transmission piston slidably mounted in said housing and operably engaging said first ends of said first and second springs;

e. means responsive to movement of the vehicle body for generating a front body angle signal, said front body angle signal generating means including a front body angle transmission piston operably engaging said second end of said first spring and secured within said housing and being connected to said front signal generating means movement longitudinally in response to vertical for movement of the front of the vehicle body relative to the vehicle point ground wheels;

f. means responsive to movement of the vehicle body for generating a rear body angle signal, said rear body angle signal generating means including a rear body angle transmission pistonconnected to slide longitudinally of said housing in response to vertical movement of the rear of the vehicle body relative to the vehicle rear ground wheels, said second spring being compressed between said output signal transmission piston and said rear body angle signal transmission piston;

g. lamp tilting linkage connected to said output signal transmission piston andto said at least one lamp for tilting said at least one lamp in response to movement of the vehicle body; and

h. damper means operably connected to said lamp tilting linkage for damping lamp tilting movements;

j. said rear vehicle body angle signal generating means further comprising a tubular piston support passing through said front body angle signal transmission piston and protruding from said housing for attachment to the remainder of the rear body angle signal generating means;

k. said lamp tilting linkage further including:

(ka) a diametrically extending pin on said output signal transmission piston;

(kb) a piston rod mounted slidably within said tubular piston support;

(kc) a pair of diametrically opposed slots extending longitudinally of said tubular piston support and slidably receiving said pin to lock the output signal transmission piston to said piston rod. 

1. In a lamp self-levelling system comprising front and rear vehicle body angle signal generating means, and a lamp tilting linkage connected to at least one lamp to be levelled; signal mixing means operably connected to said vehicle body angle signal generating means and said lamp tilting linkage; a pair of springs in said mixing means operably connecting the lamp tilting linkage with respective ones of the front and rear body angle signal generating means; adjuster means in at least one of said front and rear body angle signal generating means for initially prestressing said springs; and indicator means responsive to the strain of said springs for indicating when the prestressing of said springs by said adjustor means has attained a strain value equivalent to a predetermined operating stress value.
 2. A system as set forth in claim 1, wherein said signal mixing means includes a housing and an elongate member extending into said housing for connection to one of said springs, the other spring being connected to said housing, wherein said adjuster means is effective to modify the rear body angle signal to stress said springs and wherein said indicating means comprises a pin loosely extending transversely through said elongate member and frictionally held in position by the strain in said springs at a position such that adjustment of the rear body angle signal generating means to said predetermined strain will expand the springs and allow the pin to fall from the elongate member.
 3. A vehicle including a lamp self-levelling system, and comprising ground wheels and a body, at least one lamp to be levelled, means for sensing the angle of the vehicle body relative to the ground wheels, means for effecting pivoting of said at least one vehicle lamp about a horizontal axis in response to said angle to retain the lamp beam at a constant inclination relative to the ground wheels, and means for damping movement of said lamp, said damper comprising a cylinder having a longitudinal axis, a loose fitting two-part piston slidably mounted within said cylinder and a liquid damping medium within said cylinder damping movement of said piston along said cylinder, said piston comprising first and second parts, means biasing said first and second parts apart, respective through passage means in said first and second parts defining together tortuous fluid flow passage means, said piston parts being constructed with said respective through passage means arranged at different radial distances relative to the longitudinal axis of said cylinder.
 4. A vehicle having a front suspension anti-roll bar extending transversely of the vehicle, a rear axle and a lamp self-levelling system comprising: a. at least one lamp to be levelled; b. an arm extending vertically from the front anti-roll bar; c. a cylindrical housing; d. pivot means for hooking said housing to said arm at a location remote from the front anti-roll bar; e. an output signal piston slidably carried within said housing; f. a lamp tilting linkage connected to said output signal piston and to said at least one lamp; g. a first coil spring in said housing and having a first enD connected to said output signal piston and a second end connected to said housing; h. a second coil spring in said housing and having first and second ends, said first end being operably connected to said output signal piston; i. a cable having a first end operably connected to the second end of said second spring and having a second end disposed at a location on the vehicle remote from said housing; and j. means operably connecting said second end of the cable with said rear axle for pulling said second end of the cable away from said housing in response to a vertical movement of the rear of the vehicle body.
 5. A vehicle as set forth in claim 4 wherein said means operably connecting the second end of said cable with the rear axle comprises an L-shaped arm having a first limb resting on the rear axle and a second limb operably connected to said second end of the cable, and a bracket secured to the vehicle body supporting said arm for pivoting movement whereby raising of the vehicle rear ground wheels relative to the vehicle body effects rearward movement of said second limb relative to the vehicle body.
 6. A vehicle as set forth in claim 4 and including a rear body angle signal transmission piston slidable within said housing, said second spring being compressed between said output signal transmission piston and said rear body angle signal transmission piston; and a front body angle signal transmission abutment member secured within said housing, the said first spring being compressed between said output signal transmission piston and said front body angle signal transmission abutment member.
 7. A vehicle having a lamp self-levelling system comprising: a. at least one lamp to be levelled; b. a cylindrical housing; c. first and second springs in said cylindrical housing and each having first and second ends; d. an output signal transmission piston slidably mounted in said housing and operably engaging said first ends of said first and second springs; e. means responsive to movement of the vehicle body for generating a front body angle signal, said front body angle signal generating means including a front body angle transmission piston operably engaging said second end of said first spring and secured within said housing and being connected to said front signal generating means movement longitudinally in response to vertical for movement of the front of the vehicle body relative to the vehicle point ground wheels; f. means responsive to movement of the vehicle body for generating a rear body angle signal, said rear body angle signal generating means including a rear body angle transmission piston connected to slide longitudinally of said housing in response to vertical movement of the rear of the vehicle body relative to the vehicle rear ground wheels, said second spring being compressed between said output signal transmission piston and said rear body angle signal transmission piston; g. lamp tilting linkage connected to said output signal transmission piston and to said at least one lamp for tilting said at least one lamp in response to movement of the vehicle body; and h. damper means operably connected to said lamp tilting linkage for damping lamp tilting movements; j. said rear vehicle body angle signal generating means further comprising a tubular piston support passing through said front body angle signal transmission piston and protruding from said housing for attachment to the remainder of the rear body angle signal generating means; k. said lamp tilting linkage further including: (ka) a diametrically extending pin on said output signal transmission piston; (kb) a piston rod mounted slidably within said tubular piston support; (kc) a pair of diametrically opposed slots extending longitudinally of said tubular piston support and slidably receiving said pin to lock the output signal transmission piston to said piston rod. 